Tape printing devices of the type to which this invention pertains are disclosed in U.S. Pat. Nos. 4,927,278 & 4,966,476, assigned to Brother KK, and also in U.S. Pat. No. 4,815,871 assigned to Varitronic. The printers each include a printing device with a cassette receiving bay for receiving a cassette or tape holding case. In the '871 patent, the tape holding case houses an ink ribbon, a transparent image receiving tape and a double-sided adhesive tape which is secured at one of its adhesive coated sides to the image tape after printing, with a backing paper which can be peeled from its other adhesive side. With both of these devices, the image transfer medium (ink ribbon) and an image receiving tape (substrate) are in the same cassette.
Another type of tape printing device is described, for example, in U.S. Pat. No. 5,458,423, the contents of which are incorporated herein by reference. With this printing device, the substrate tape is similar to that described in the '871 patent, but is housed in its own tape holding case and the ink ribbon is also housed in its own tape holding case.
In all these cases, the image receiving tape overlaps with the ink ribbon and passes through a print zone consisting of a fixed print head and a platen against which the print head can be pressed to transfer an image from the ink ribbon to the image receiving tape. There are many ways to do this, including dry lettering or dry film impression. At present, however, the most common method is thermal printing. In thermal printing, the print head is heated and the heat causes ink from the ink ribbon to be transferred to the ink receiving tape. Alternatively, the print head can come into direct contact with a thermally sensitive image receiving tape. Heating the print head then produces an image on the image receiving tape.
U.S. Pat. No. 5,395,173 discloses a tape printer which is capable of printing text as well as bar codes. As is known to those skilled in the art, bar codes, which typically comprise a number of lines of varying thickness, are commonly used in article identification systems. A device according to the '173 patent allows a user to type in the text data which is to be printed as ordinary text, as well as the bar code data, which is to printed out as a bar code.
The device has two modes, a normal mode and a special mode. In the normal mode, the text data is displayed as such while the bar code data is represented by specially assigned characters. Only text data can be entered in normal mode. If the user wishes to insert bar codes along with text, the user presses a bar code key. The tape printer then switches to a special mode, in which only bar code data can be entered and displayed. After the bar code data has been entered, the user presses the execution key and the printer switches back to the original, normal input and display mode. The bar code data is then stored in the printer memory, e.g., an input buffer along with the text data. The bar code data is distinguished from the text data by means of a start code and an end code, which are stored just before and after the bar code data.
One disadvantage of the prior art is that it is not possible to see both ordinary characters and bar code data simultaneously on the display. For this reason it is not possible to control both ordinary characters and bar code data at the same time. Therefore the user must switch into the special mode if he wants to control or edit the number to be printed as a bar code.
Another disadvantage is that the bar code start and end codes require valuable space in the input buffer of the printer's memory. This reduces the total number of characters which can be stored in a fixed-length input buffer.
A further disadvantage is that bar code data conversion during printing is more complicated due to the bar code start and end codes. This is because each time a character is read out of the memory, the conversion device must first determine whether the character is a bar code start code, a bar code end code, or something else. This step unnecessarily lengthens the conversion time.